Many digital circuits require a clock or clock signal to operate. Often an oscillator is used to generate the clock signal. These oscillators typically include a crystal that vibrates in response to a voltage to generate the clock signal. Often the crystal is a quartz crystal.
Some applications or systems require that the clock frequency have a relatively high degree of stability compared to that required by most consumer systems. For example, some military applications require a higher degree of frequency stability compared to a computer or smart phone of an average user. For instance, a radar system may require a very stable reference frequency to operate. As another example, some computing networks require a higher degree frequency stability for synchronization purposes compared to certain stand-alone computing systems.